The Nearctic members of the genus Platycheirus Lepeletier and Serville are revised. Five species, Platycheirus alpigenus Nielsen and Barkalov, Platycheirus brunnifrons Nielsen, Platycheirus clausseni Nielsen, Platycheirus speighti Doczkal, Stuke, and Goeldlin, and Platycheirus splendidus Rotheray, are newly recorded for the Nearctic Region, while three species, Platycheirus sp. trichopus, Platycheirus sp. “hyperboreus dark form” and Platycheirus n. sp. “perpallidus1” are new manuscript names. Females of 42 species are described for the first time. The genus Pyrophaena Schiner is resurrected. The genus Tuberculanostoma Fluke is synonymized with Platycheirus. An illustrated key to all 73 males and 52 females of Platycheirus and the males and females of the 3 species of Pyrophaena occurring in the Nearctic region is provided. Morphological and combined morphological/molecular COI phylogenetic analyses of the Platycheirus albimanus group are presented, as well as a molecular analysis of all available Platycheirus COI sequences. The species groups within Platycheirus are redefined based on these analyses. / NSERC-CANPOLIN

Chapter 1. The family Pteronarcyidae (Plecoptera) is a highly studied group of stoneflies and very important to a wide variety of aquatic studies. Several phylogenies have been proposed for this group recent decades, however there is little congruence between the various topologies. The present study revises the phylogeny of the group by combining molecular data from mitochondrial cytochrome oxidase subunit II, ribosomal subunit 12S, ribosomal subunit 16S, and nuclear loci ribosomal subinit 18S and Histone H3, with published morphological data in a parsimony-based total evidence analysis. The analysis produced a well-supported phylogeny with novel relationships within the genus Pteronarcys. Maximum Likelihood and Bayesian analyses produced topologies congruent with parsimony analysis. Character mapping revealed several homoplasious morphological characters that were previously thought to be homologous. Chapter 2. Phylogeographic studies in aquatic insects provide valuable insights into mechanisms that shape the genetic structure of aquatic communities. Yet studies that include broad geographic areas are uncommon for this group. We conducted a broad scale phylogeographic analysis of P. badia across western North America. In order to allow us to generate a larger mitochondrial data set, we used 454 seqeuncing to reconstruct the complete mitochondrial genome in the early stages of the project. Our analysis reveals what appears to be a complex history of isolation and multiple invasions among some lineages. The study provides evidence of multiple glacial refugia and suggests that historical climactic isolations have been important mechanisms in determining genetic structure of insects in western North America. Our ability to generate a large mitochondrial data set through mitochondrial genome reconstruction greatly improved nodal support of our mitochondrial gene tree, and allowed us to make stronger inference of relationships between lineages and timing of divergence events.